1. Field of the Invention
This invention relates to a rotary chuck of the type used to clamp a workpiece to the rotating shaft of a machine tool in order to profile the workpiece using a cutting tool of one kind or another. It relates more particularly to a so-called universal chuck having a plurality of jaws which move in unison.
2. Background Information
Conventional universal chucks of this general type include a main body or housing having a plurality of keyways formed in the housing which are angularly spaced around, and radiate away from, the rotary axis of the housing and a corresponding plurality of jaw assemblies slidably received in the keyways. Invariably, each jaw assembly includes an inner or master jaw which extends substantially the entire height of the associated keyway and an outer or slave jaw which is releasably fastened to the inner jaw exterior to the housing by at least one fastener which extends through the outer jaw and is threaded into the inner jaw. Each outer jaw has clamping surfaces extending in the general direction of the axis and the surfaces of all the outer jaws collectively form a split ring able to grip a workpiece from the outside by moving the jaw assemblies simultaneously radially inward toward said axis and from the inside by moving the jaw assemblies simultaneously radially outward away from the axis. A typical chuck may have many sets of outer jaws of various shapes and sizes to enable the chuck to clamp to a variety of different workpieces.
In most prior chucks, the jaw assemblies are moved along the keyways between radially inner and outer positions by rotating a pinion in the side of the chuck housing. There also exist chucks which open and close the jaw assemblies using a so-called tommy bar in lieu of a pinion which is rotatable about said axis relative to the housing. Both the pinion and the tommy bar are geared to the master jaws so that when they are rotated in one direction or the other, the jaw assemblies are moved radially in or out along the keyways.
The prior chucks are disadvantaged in that their outer jaws are secured to their inner jaws by threaded fasteners. This means that when it is necessary to change the outer jaws to accommodate a different workpiece, the fasteners in all of the jaw assemblies must be unscrewed to enable removal of the existing outer jaws and then screwed back in and tightened with the proper torque to secure the new set of outer jaws. Considering that some chucks may have as many as six jaw assemblies, the replacement of the outer jaws of a given chuck can be a tedious and time consuming task. Also, during the jaw replacement process there is a great potential for one or more fasteners to be soiled, misplaced or lost thereby prolonging the process and extending the downtime of the associated machine tool. The replacement of the jaws is particularly arduous for less skilled workers and those with some loss of manual dexterity.
Another drawback of the prior chucks is that it takes several revolutions of the pinion in order to move the jaw assemblies a significant distance along their respective keyways. Therefore, the act of clamping the chuck to a workpiece can take an excessive amount of time. More importantly, even when the chuck is firmly engaged to the workpiece, there is a limit to the amount of torque that can be applied to the workpiece by a cutting tool when the workpiece is being rotated. This is because, as noted above, the outer jaws of the chuck are connected to the inner jaws exterior to the housing only by way of the threaded fasteners. That is, the outer jaws are not directly connected to the housing. Therefore, during operation of the chuck, there is a potential for fastener failure which could result in an outer jaw being propelled away from the rotating chuck and causing injury and part damage.